A waterproof floor covering of this type is known from EP 1808546 of the applicant. In consideration of the increasingly stricter ecological requirements or motivations for saving materials, weight and energy, amongst others, the need arises for thinner panels, yet still with sufficient strength and shape retention and with sufficiently strong coupling or connecting elements at their edges of the panels or tiles with adjacent panels or tiles. In the relatively thick core layer of the extruded panels, according to EP 1808546, closed air channels have previously been created. Nonetheless, the weight of these panels remains too high.
Thus the need has arisen for such panels that can be designed to be almost 15% to 20% lighter. Besides that, there is an increasing, more important, ecological need for using as much recycled material as possible for the panels and as efficiently as possible. However, the application of at least a considerable portion of recycled synthetic materials, e.g. recycled PVC in the synthetic materials, creates the risk of obtaining plates with uneven strength and local differences of other characteristics spread over their volume. The recycled synthetic plastic material can be in the form of ground materials, micronized powder-shaped particles or pre-extruded synthetic strands, e.g. made of such ground materials and powder-shaped particles and of mixed granules cut from them. However, these particles or even granules of recycled synthetic material, as starting material to use, do not all have the same composition and characteristics. According to their volume, density, composition and previous use, they can comprise more or less filler materials of various compositions and shapes, both for pre-consumptive as post-consumptive recycling. Furthermore, post-consumptive recycling material often contains an extra tarnishing with the presence of foreign particles, or—for example due to ageing—the properties of the polymer sensitively deviate from new, freshly prepared polymers. Therefore, when melting and mixing upstream of the extrusion nozzles in the screw press, one obtains a melted mass with more or less heterogeneous characteristics throughout its volume, in other words characteristics that could sensitively deviate in local places in the melted mass, e.g. with regard to viscosity or rheology. This can result in varying flow patterns and/or flow rate fluctuations in the molten mass by the supply to, and passage through, the extrusion nozzles and during the passage of the cooling molten mass into the adjacent cooled calibration section.
In this way it becomes difficult to continuously realize a sufficiently and evenly dense filling over the entire width of the passage opening of the extrusion nozzle and in particular to produce a support plate with an even and flat top surface. By an even surface in this context is meant a surface on which potential irregularities protrude less than 100 microns, preferably less than 50 microns, above or under the (theoretically) intended surface level. However the realization of a support plate with such an evenly extruded top surface is necessary for guaranteeing a sufficient even top surface for the subsequent attachment of a waterproof and wear-resistant coating, and therefore also for the covering panel. Furthermore, the satisfactory imperviousness and other characteristics of the extruded support plate, according to EP 1808546, may not decrease—on the contrary.
According to EP 1808546 the opposite sides of the relatively thick panels are fitted with complementary profile edges in the shape of a tongue on the one hand, and in the shape of a groove on the other hand. The groove is bordered by an upper-lip and a lower-lip. As such the coupling or connection of adjacent panels takes place through an insertion process of the tongue on the edge of a panel into the complementary groove on the edge of an adjacent panel in a direction that is approximately parallel to the top surface of the panel. The thinner the panel the smaller also the thickness is of the tongue and of these lips that border the groove. Thus, the panel thickness cannot be reduced to below a limit whereby the connection or coupling strength of said tongue between the groove edges would become insufficient. Nonetheless, the need for extremely thin panels or tiles remains, while the strength of the tongue-in-groove connection, according to EP 1808546, possibly no longer suffices and for which another connection configuration would have to be applied.
Thus the invention has as an aim to provide an improved impermeable panel of the type known from EP 1808546 with an extruded support plate made of synthetic plastic material with a small to extremely small thickness, yet whereby the support plate and the border connections are still sufficiently strong. After all, the connections have to clamp or anchor sufficiently, at least in a cross direction (perpendicular) to the top surface for the purpose of being able to realize a durable and very flat transition between the consecutive panels in the wall covering. Moreover, when using thinner panels, the need to subsequently disconnect them from the assembled or installed wall-covering to replace them or to disassemble and reuse the covering elsewhere, remains. For this purpose, the invention also aims to use as much recycled synthetic plastics as possible—even as much as 100% of its weight—yet still preferably obtaining support plates with a very even top surface. Furthermore, the panels should preferably also have a strong sound insulating capacity.